The invention lies in the field of semiconductors. The invention relates to a semiconductor component with a semiconductor chip having contact pads on a first main face, a wiring foil with recesses for the contact pads applied to the first main face and having, on a side facing away from the first main side of the semiconductor chip, conductor tracks for connecting the contact pads to solder contacts. The contact pads located in the at least one recess are electrically connected through wire connections to adjacent conductor track ends and each wire connection is surrounded by a sealing compound. The invention also relates to a method for manufacturing such a semiconductor component.
Semiconductor components with a board on chip (xe2x80x9cBOCxe2x80x9d) housing are applied to a carrier substrate using a ball grid array (xe2x80x9cBGAxe2x80x9d) and are electrically connected to it. The characterizing feature of these BOC housings is a wiring foil having conductor tracks on a side facing away from the first main side of the semiconductor chip, which conductor tracks end in the vicinity of the recesses of the wiring foil. The at least one recess in the foil permits the end of the conductor track to be electrically connected by a bonding wire to the contact pad or pads located in the recess. A solder stop mask, in which there are recesses for the other ends of the conductor tracks, is usually applied to the conductor tracks. A solder contact is electrically conductively connected to these exposed ends of the conductor tracks. The solder contact can be embodied, for example, as a ball. To avoid damage to the bonding wires, for example, when the semiconductor component is applied to the carrier substrate (board), the recess of the contact pads and the bonding wires are completely coated with a sealing compound. The sealing compound may be, for example, an epoxide mass. It is selectively applied in a liquid state to the points on the recesses and the bonding regions of the conductor tracks and is subsequently cured. The sealing compound is used to protect the active chip structures against moisture and to provide mechanical protection to the bonding wires. The sealing must be carried out such that all the depressions are filled in without air occlusions. At the same time, the bonding wires must be covered, in particular, at the connection point to the conductor track ends. The height of the sealing compound must not exceed the diameter of the solder contacts because otherwise it would no longer be possible to make an electrical connection between the semiconductor component and the carrier substrate. The application of the sealing compound constitutes a serious problem in practice because the viscous material of the sealing compound spreads quickly, especially on the solder stop resist that is applied to the conductor tracks. The sealing compound could, thus, flow into the recess or recesses provided for the solder contacts. However, if the sealing compound gets-into these recesses, it is no longer possible to produce a reliable soldered connection between the conductor track end and the solder contact.
To avoid such a problem, the distance between the recesses for the soldered contacts and the at least one recess in which the contact pads are located can be made such a size that the sealing compound has enough xe2x80x9cflowing pathxe2x80x9d until it hardens. However, the configuration places strict limits on the miniaturization of the semiconductor component.
It is accordingly an object of the invention to provide a semiconductor component and method for manufacturing it that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that overcomes the above-mentioned disadvantages in a simple way.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a semiconductor component, including a semiconductor chip having a main face, at least one contact pad disposed on the main face, at least one wire connection, at least one solder contact, a wiring foil applied to the main face, the wiring foil having at least one recess for accommodating the at least one contact pad in the at least one recess, the wiring foil having, on a side facing away from the main side of the semiconductor chip, at least one conductor track for connecting the at least one contact pad to the at least one solder contact, the at least one conductor track having conductor track ends, the at least one contact pad electrically connected to at least one of the conductor track ends through the at least one wire connection, and a sealing compound surrounding the at least one wire connection, the sealing compound having a first layer and a second layer.
The invention proposes to have the sealing compound be made of a first layer and a second layer. Advantageously, the first layer merely fills the at least one recess in which the contact pads are located. On the other hand, the second layer covers the wire connection projecting out of the first layer, and the adjacent conductor track end. The adjacent conductor track end is understood here to be the region in which the connection is produced between the conductor track end and the wire connection. After the provision of the first and second layers, the entire wire connection including the bonding contacts is surrounded with a sealing compound. If the first layer has a low viscosity, the sealing compound can spread out in the recess without air occlusions occurring. On the other hand, the second layer advantageously has a high viscosity. Because the second layer is positioned above the edges of the recess, it would be able to spread along the conductor tracks and along a solder stop mask in the direction of the recesses for the soldered contacts. However, due to the high viscosity, the spreading takes place only very slowly so that the sealing compound can be cured before the critical regions are reached.
The invention makes it advantageously possible to keep small the distances between the at least one recess in which the contact pads are located and the recesses in which the later soldered contacts are used. The configuration permits the semiconductor component to be miniaturized.
In accordance with another feature of the invention, the at least one contact pad is electrically connected to adjacent ones of the conductor track ends through the at least one wire connection.
In accordance with a further feature of the invention, the first layer fills a maximum of the at least one recess.
In accordance with an added feature of the invention, the second layer covers the at least one wire connection projecting out of the first layer and the at least one of the conductor track ends.
In accordance with an additional feature of the invention, the first layer has a low viscosity.
In accordance with yet another feature of the invention, the second layer has a high viscosity.
The first and second layers may be made of different materials with different chemical properties. However, it is particularly advantageous if the first and second layers are made of the same material, in which case, the properties of viscosity, thixotropy, and creepage can be adjusted merely by physical properties (for example, filler content). The first layer is advantageously adjusted to a low viscosity. The adjustment makes possible a process for filling the recess without air occlusions. The second layer, which advantageously has a higher viscosity than the first layer, permits a type of xe2x80x9cglobtopxe2x80x9d to be applied without creeping onto the solder stop mask or wetting the recesses for the soldered contacts. The properties of the first and second layers can be adjusted, in particular, by different filler proportions.
In accordance with yet an added feature of the invention, there is provided a solder stop mask disposed on the at least one conductor track, the solder stop mask defining at least one recess for the at least one of the conductor track ends.
Solder balls are advantageously used as the soldered contacts, and are disposed on the wiring foil, that is to say, on the solder stop mask of the wiring foil, in the form of an array.
With the objects of the invention in view, there is also provided a method for manufacturing a semiconductor component, including the steps of:
a) applying the wiring foil to the first main side of the semiconductor chip;
b) producing the wire connection between the contact pads and the adjacent conductor track ends;
c) applying the sealing compound to locations on the at least one recess such that the wire connection is completely covered with the sealing compound; and
d) only curing the surface of the sealing compound.
As becomes clear from the following description of the manufacturing method of an alternative semiconductor component according to the invention, it is not necessary to install any additional processes in comparison with a manufacturing method according to the prior art. The processing times are also marginally longer than a manufacturing method according to the prior art.
In accordance with again another mode of the invention, there is only a short time between the first step and the second step.
In accordance with again a further mode of the invention, a surface of the sealing compound is cured in a period after application of the sealing compound and before the sealing compound, still having a low viscosity, reaches regions of solder contacts.
The manufacturing method according to the invention makes possible a semiconductor component that can be manufactured with existing processes. The sealing compound is applied to the locations on the recesses, for example, by dispensing or printing. The surface advantageously cures within a predetermined period after the application of the sealing compound, the period being dimensioned such that the sealing compound that still has low viscosity after the application has not yet reached the regions of the soldered contacts. The curing of the surface reduces the viscosity of the sealing compound to such an extent that either a type of xe2x80x9cskinxe2x80x9d forms or the sealing compound on the surface becomes so viscous that it is no longer capable of flowing. As a result, the compound is prevented from running in the direction of the recesses for the soldered contacts. It is, thus, also possible to miniaturize the semiconductor component. However, because the curing according to the invention occurs only at the surface, the sealing compound retains its original flow properties in the interior. As such, the compound can flow on and reliably fill in the cavities so that no air occlusions occur.
The curing of the surface can be performed, for example, by briefly heating the sealing compound. As an alternative, it is conceivable to implement the curing by spraying with a curing agent or a sprayable sealing compound with a higher proportion of filler or a catalyst. In another alternative, it is conceivable to cure the surface by irradiating with infrared light. After the sealing compound has finished flowing in the recess in which the contact pads are located, a concluding curing step can be carried out so that the entire sealing compound is hardened.
In accordance with a concomitant feature of the invention, the application of the sealing compound includes filling in the at least one recess in a first step and applying the sealing cap in a second step. It is advantageous if there is a short waiting time between the first and second steps. The procedure permits distance tolerances to be set between the first main side of the semiconductor chip and the height of the sealing cap. In addition, the risk of the formation of bubbles in the recess is reduced.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor component and method for manufacturing it, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.